The proposed invention relates to the headlights and lamps of an automobile comprising LED light sources. The light output of the headlights or lamps of automobiles, and hence the LED sources, must comply with definite legal and other requirements under various working conditions. This is provided by the LED drive module (LDM), which supplies the correct current to the LEDs and also ensures their protection.
The modern light sources of automobiles focus on optical performance, style and appearance, as well as modern technologies such as LED sources and the like. The design of these elements is as a result becoming increasingly more complex and complicated.
The driving or control of LEDs (light emitting diodes) is one of the main tasks in the electronic development. Current sources are used predominantly for the driving of individual LEDs, or LED strings or fields. Three main categories of these sources or regulators are customarily used: resistor, linear, and switching sources. Each of these architectures has its advantages and its disadvantages, relating especially to cost, efficiency, and functionality.
A resistor regulator is composed in particular of resistors hooked up in series with LED diodes. The main advantage of this solution is its low price and simplicity. The main disadvantage is that the regulator does not ensure a constant current, or light output, and it has low efficiency. The linear regulator already contains semiconductor components. This type of regulator is able to provide a constant current or light output in a defined range of input voltages and still at relatively low price. The drawback is its low efficiency. Switched sources are the most complex, being generally based on specialized integrated circuits. This type of regulator is able to provide a stable light output or current in a broad range of input voltages, it enables the driving of many interconnected LEDs, and it attains high efficiencies. The drawback is the high price and the complexity of the design.
The closest architecture to the proposed design is an application where the lamp control unit (Body Control Module—BCM) generates a pulse-width modulated (PWM) signal in dependence on the voltage in the automobile's network, which drives the lamp unit that is provided with a linear or a resistor source. The use of PWM in the BCM brings several disadvantages. In event of a malfunctioning of the PWM, the lamp unit is not protected against voltage surge, which leads to further expenses for its protection. The individual transfer characteristic of the PWM versus the input voltage is not defined according to the requirements of the given lamp unit (the same BCM is used for many automobiles), and the BCM in PWM mode may cause increased electromagnetic interference in view of the high pulse currents. The topologies when PWM is generated in the BCM do not allow a combination of current surge protection with the use of a switching transistor working in linear duty.
A specific solution making use of pulse generators with PWM, although with use of different characteristics or a different effect and function, is JP2003317978A, i.e., a design of the vehicle lighting by means of parallel strings with LED diodes, utilizing a pulse generator of PWM switching a transistor by width modulation, but controlled from the output terminal S across an input voltage detection circuit and by feedback obtained from the connected cathodes of the LED diodes, or US2011156605, where each string has its own switching MOSFET transistor controlled by a unit with PWM.